If it was overfueling the exhaust should be blacker, not white rich = more carbon and you should have a lot of black on the back of the car. Like I said, how old is the cat back? Also if it is new there could be contaminants burning off from joints. I had my ECU (V3 Sti) take over 3 weeks to adjust itself to a different 3" TBE, it had a fairly basic 3" on before this with the same config cat/centre reson/rear muffler...their fussy!

I take it when you say re-learning you're getting some hunting at idle?